Organogelator-Templated Synthesis of Hollow TiO 2 Nanotubes
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n of Ru-Ni Binary Nanoparticles into Dendrimers Enhances Catalytic Activity A team of researchers at Pohang University of Science and Technology in MRS BULLETIN/AUGUST 2000
Korea have obtained Ru-Ni binary nanoparticles by electrodeposition of the metals encapsulated in dendrimers that showed significantly enhanced catalytic activities for the oxidation of ethanol when compared with bulk metal-oxide electrodes. Incorporation of functional groups like amines enables the dendrimers to function as complexing agents of transition metals. “The dendrimers act as both nanoscale templates and separators between the particles,” said Su-Moon Park, professor at Pohang. Therefore, he expected nanoparticles prepared in this way to offer advantages for use as electrocatalysts due to large surface areas, small catalyst loading, and inhibition of aggregation between particles. Having demonstrated before that Ru-Ni mixed oxides are potent electron-transfer mediators for the electro-oxidation of ethanol, his group attempted the synthesis of dendrimertemplated Ru-Ni nanoparticles. As reported in the August issue of Electrochemical and Solid-State Letters, the Ru-Ni binary nanoparticles were prepared by potentiostatic electrodeposition in a mixed solution containing amine-terminated poly(amidoamine) dendrimers (G4(NH2), where G4 represents the fourth generation) with Ru(III) ions and Ni(0) loaded into G5(OH) dendrimers. The Ni21-G5(OH) was pre-reduced with NaBH4. The particles showed an absorption peak arising from a Mie plasmon resonance in their UV-visible spectra, indicating that the particles were larger than the Mie-onset particle diameter of 5 nm. The blue shift of the plasmon band on progressive deposition suggested that the metal ions were deposited later as nanoparticles. Cyclic voltammograms of pure Ni or pure Ru dendrimers were similar to those for bulk metals and did not show current saturation at ethanol concentrations up to 1.0 M. “But for the Ni-Ru binary particles, the nucleation current loop appears when the ethanol concentration is greater than 0.05 M,” said Jae-Woo Kim, a doctoral student at Pohang. “This suggests that the formation of the passive film is faster than the chemical decomposition reaction subsequent to its formation.” Polarization resistances of these electrodes calculated from impedance responses showed a decrease from 460 Ω cm2 to 31 Ω cm2 upon addition of ethanol, indicating a significant catalytic activity for ethanol oxidation. Electrochemical experiments revealed a very fast redox reaction of the templated nanoparticles, with exchange currents for ethanol oxidation being improved by a few orders of magnitude when compared with a bulk electrode.
Park and his student agree that “nanoparticles prepared using dendrimer templates are promising candidates for oxidation of organic compounds.” In further studies, they plan to investigate the morphology of nanoparticles electrodeposited under experimental conditions. CORA LIND
Organogelator-Templated Synthesis of Hollow TiO2 Nanotubes Nanostructured anat
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